High power laser diodes have been developed for many applications, including solid-state laser pumping, fiber laser pumping, and material processing. The spectral bandwidth of high power diodes is typically spread over the range of 3-5 nm. A narrower emission spectrum in the range of 0.1-0.5 nm and a smaller wavelength tolerance, however, can be extremely beneficial for special applications, such as spin exchange optical pumping (SEOP). SEOP has various diverse applications, including applications in nuclear physics, atomic physics, laser cooling, medical resonance imaging, and neutron scattering.
One example application for such diode lasers is the optical pumping of alkali metal vapors, typically rubidium. Such optical pumping can be used to polarize various atoms, such as 3He or 129Xe atoms. For instance, using SEOP, unpaired rubidium electrons can be polarized by laser, and then the polarization of electron is transferred to 3He atoms via hyperfine interaction. The polarized 3He gas can be used, for instance, as a neutron spin filter (NSF) in polarized neutron scattering experiments.
In order for SEOP to be successful over relatively long time periods, however, high-power spectrally narrowed lasers with good stability are highly desirable. For example, in order to achieve high efficiency optical pumping, it is desirable for the spectral bandwidth of the high-power laser to match the pressure-broadened D1 absorption line of rubidium vapor. When the spectral bandwidth of a laser matches the pressure-broadened absorption line-width of rubidium vapor, even a small drift of the center wavelength (e.g., 10% of spectral line-width) will greatly reduce the efficiency of the laser. The long term stability of a line-width matched laser is therefore desirable for many SEOP applications, including neutron spin filters (NSFs). Additionally, it is desirable for a SEOP laser system to be easily integrated into an in situ SEOP system.